Ústav teoretické a aplikované mechaniky Akademie věd ČR

The Institute of Theoretical and Applied Mechanics AS CR, v. v. i
(ITAM AS CR, v. v. i.)

Domain 4:

Analysis and modelling of particular and cemented materials and environments

Selection of a material model plays a key role in the numerical simulation of boundary value problems in geotechnical engineering (e.g.
bearing capacity of foundations or deformations in the vicinity of deep excavations). Therefore, development and testing of constitutive models is a major research task of the Laboratory of Soil Mechanics ITAM.

Due to the complexity of the phenomena observable for various types of soils it is not possible to define a unique approach leading to a perfect model. It is always necessary to take into account specific features and ways of loading of particular geomaterials. The research at ITAM concentrates on structural phenomena and formulations in the framework of hypoplasticity. The hypoplastic approach represents a relatively new model which does not distinguish between elastic and plastic deformations. Incorporation of critical states (e.g. Kolymbas et al., 1995) enables a consistent way of describing of noncohesive soils of different densities, and simplifies the calibration of material parameters (Herle and Gudehus, 1999). The cyclic behaviour can be described by introducing a further state variable, so-called intergranular strain (Niemunis and Herle, 1997). At present, the research is focused on enhancing the model for cohesive and cemented soils. Another research direction covers implementation of the model into FEM and evaluation of its influence in simulations of boundary value problems.

The geotechnical part of the research activity involves fundamental research and developing theories of lateral pressure of multi-phase granular materials together with designs theories, especially Limit State Design. In spite of the focus on the theoretical research, the results are directly useable for implementation in codes and standards.

The concept of a new, more general "General Lateral Pressure Theory" has been elaborated and is being verified and further developed by physical and numerical experiments. Due to the originality of the conception, the new original experimental equipment, instruments and computing programmes have had to be developed. The development of very advanced concepts of computing programmes is supported. At present, the stand is being modernised, the monitoring of the pressure and movements of the arbitrarily moved wall are being digitised and adapted for computer drawings. The new stand set-up will enable arbitrarily slow and continuous movement of the retaining wall, which will be drawn, monitored and recorded by the computer, as will the contact pressures.
The two components (normal and shear vertical) of the contact pressures are monitored separately, using the Czech invention of a two-component sensor (Šmíd-Novosad). The development of a three-component pressure sensor (normal, shear vertical and moment) is near to completion.

Work on design theories concentrates on Limit State Theory connected with the upcoming implementation of European Building Codes, especially EUROCODE 7-1 "Geotechnical design". A number of analyses carried out by us and by other scientists and engineers have shown that EC 7-1 is less suitable and less effective than contemporary Czech standards.
Acceptance of EC7-1 without the changes and appendices in the National Annex would be a retrograde step. Present-day Limit State Theory does not take into account the special character of geotechnics and granular materials. Thus, the basis of Limit State Theory, i.e. definitions of the characteristic and design values, is being verified. The development of appropriate alternative design approaches has already begun.

Interdisciplinary problems of architectural heritage materials.

Research at ITAM focuses on physical properties of historic materials, particularly on properties of lime mortars (Válek J. 2000), fibre reinforced mortars and their modern substitutes (Drdácky M. et al.
2003), in-situ testing of renders, mortars and historic masonry. It also involves work on problems of compatibility of new renders with historic renders and masonry.